Markers for a medical ultrasound imaging catheter

ABSTRACT

A catheter is provided for medical ultrasound imaging that can be effectively used in combination with other imaging modalities to detect medical structures of interest as well as the catheter. Markers are added to the catheter with precision, which provides a means to merge the images from different modalities. Using a template, apertures for marker placement are formed in the catheter after creating the catheter housing. The ultrasound array may be used for accurate positioning of the template. Alternatively or additionally, a rigid insert with markers connects with the array. The insert holds the markers in place and may reduce artifacts in ultrasound scanning due to flexing of the array.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional and claims benefit of priority under 35USC 120 to pending U.S. patent application Ser. No. 13/369,236, filedFeb. 8, 2012.

BACKGROUND

The present embodiments relate to medical ultrasound imaging catheters.An acoustic array is positioned in a catheter. The catheter ispositioned in the patient, such as in the heart of the patient. Thepatient is scanned using the acoustic array, providing real-time imagesfrom within the patient. The ultrasound imaging may assist withdiagnosis or treatment. However, the flexibility of the acoustic arraymay result in artifacts in the image. The images may have speckle noiseor other artifacts, so it may be difficult for a physician to relate theultrasound image to the region to diagnose or treat.

Fusing fluoroscopy with the ultrasound imaging provides more informationfor diagnosis or treatment. The patient and catheter are imaged usingx-rays. To register the fluoroscopy imaging with the ultrasound imaging,the catheter is located within a fluoroscopy image. Location of thecatheter may be difficult to determine, so radio opaque markers areadded to the catheter. The markers allow more precise locationidentification of the catheter in the fluoroscopy image. Accurateplacement of the markers is needed.

The markers are positioned during catheter construction. The catheterhousing is formed over the markers and relied on to hold the markers inplace. However, the housing is not stable or flows during theconstruction of the catheter. The markers positioned in the catheterduring the construction may change position, leading to inaccuracies inregistration of the fluoroscopy and ultrasound images.

For tracking an imaging catheter with magnetic position sensors, ametallic stiffener is provided in the catheter. The stiffener mayimprove imaging while also improving the orientation of the magneticposition sensors and the acoustic array.

BRIEF SUMMARY

By way of introduction, the preferred embodiments described belowinclude methods, systems, improvements, and catheters for medicalultrasound imaging. Markers are added to the catheter with someprecision. Using a template, apertures for marker placement are formedin the catheter after forming of the catheter housing. To position thetemplate before forming the apertures, the ultrasound array may be used.Alternatively or additionally, a rigid insert with markers connects withthe array prior to forming the catheter housing. The insert holds themarkers in place during flow of the catheter housing and may reduceartifacts in ultrasound scanning due to flexing of the array.

In a first aspect, a method is provided for manufacturing a medicalultrasound imaging catheter. A catheter housing is positioned relativeto a template. The catheter housing houses an array of ultrasoundelements. The template includes at least one first aperture. Thepositioning places the first aperture to be near but not on the array. Amarker aperture is formed in the catheter housing using the firstaperture of the template. A marker is inserted in the marker aperture.The catheter housing is sealed around the marker.

In a second aspect, a system is provided for inserting a marker in amedical ultrasound imaging catheter. A clamp is configured to hold themedical ultrasound imaging catheter in a position relative to a guide.The guide includes a through hole.

In a third aspect, a method is provided for manufacturing a medicalultrasound imaging catheter. An insert is positioned adjacent to atransducer array. The insert has a marker. The transducer array isconnected with the insert such that the marker is adjacent to thetransducer array in a distal or proximal direction relative to themedical ultrasound imaging catheter. A housing of the medical ultrasoundimaging catheter is formed over the transducer array, insert, andmarker.

In a fourth aspect, a system is provided for manufacturing a medicalultrasound imaging catheter. An insert has a cavity and at least onemarker adjacent to the cavity. A transducer array is sized to fit withinthe cavity.

The present invention is defined by the following claims, and nothing inthis section should be taken as a limitation on those claims. Furtheraspects and advantages of the invention are discussed below inconjunction with the preferred embodiments and may be later claimedindependently or in combination.

BRIEF DESCRIPTION OF THE DRAWINGS

The components and the figures are not necessarily to scale, emphasisinstead being placed upon illustrating the principles of the invention.Moreover, in the figures, like reference numerals designatecorresponding parts throughout the different views.

FIG. 1 is a block diagram of one embodiment of a system for a medicalultrasound imaging catheter;

FIG. 2 is a perspective view of one embodiment of a guide and catheterfor manufacturing the catheter with markers;

FIG. 3 is a perspective view of another embodiment of a guide andcatheter for manufacturing the catheter with markers;

FIG. 4 is a flow chart diagram of one embodiment of a method formanufacturing a medical ultrasound imaging catheter;

FIG. 5 is a cross-sectional view of a compression fitting for holdingthe catheter according to one embodiment;

FIG. 6 is a side view of one embodiment of a system for manufacturing amedical ultrasound imaging catheter; and

FIG. 7 is a flow chart diagram of one embodiment of a method formanufacturing a medical ultrasound imaging catheter.

DETAILED DESCRIPTION OF THE DRAWINGS AND PRESENTLY PREFERRED EMBODIMENTS

To insert markers within an ultrasound catheter, a cylindrical templatefits over the catheter. Holes may be drilled into the plastic catheterbody using the cylindrical template as a guide. Markers made from radioopaque material (e.g., tungsten or silver) are inserted into the drilledholes. The markers provide guidance for registration or detection of thecatheter in fluoroscopic images.

An additional or alternative approach is to add an insert to thecatheter. The insert supports or is connected to the ultrasoundtransducer array. The insert extends beyond the array distally and/orproximally. One or more markers are in the extension of the insert. Thecatheter housing is formed over the array, insert, and markers.

While x-ray markers are described herein, other types of markers may beused. For example, the catheter is to be detected in magnetic resonanceimaging, optical imaging, or other imaging using non-x-ray radiation.Markers of material with high contrast or opaque to the type of imagingare added to the catheter using the template or added insert.

FIG. 1 shows a system for medical ultrasound imaging with a catheterhaving markers 58. The ultrasound imaging system is used for diagnosisand/or treatment in combination with another imaging modality, such asan x-ray, fluoroscopy, magnetic resonance, computed tomography, oroptical system. Both imaging modalities scan a patient for generatingimages to assist a physician.

The ultrasound imaging system includes the array 12 of elements 24 formedical ultrasound, a beamformer 52, an image processor 54, and adisplay 56. Additional, different, or fewer components may be provided.For example, the system includes the array 12 in a catheter 50 withoutthe beamformer 52, image processor 54, and/or display 56. These imagingelectronics may be in a separate ultrasound imaging system. Thetransducer and catheter 50 releasably connect with the imaging system.

The array 12 is used in a transducer probe, such as a medical ultrasoundtransducer. The transducer is used within a patient, such as a catheter50, a transesophageal, vaginal, intercavity, intraoperative, or otherprobe. Alternatively, the transducer probe is used outside of a patient,such as a handheld transducer probe. The array 12 is connected with orpositioned in the transducer probe. An acoustic window or lens coversthe array 12 to allow acoustic scanning from an emitting face 22 of thearray 12 from within the probe. In the catheter embodiments, the windowis the housing of the catheter 50.

The array 12 has a plurality of elements 24, backing block, electrodes,and a matching layer. Additional, different, or fewer components may beprovided. For example, two or more matching layers are used. The backingblock material absorbs acoustic energy to limit or prevent reflectionsreceived from the back of the array 12. The matching layers provide amore gradual transition between acoustic impedance, minimizingreflection from the boundary between the transducer and the patient. Theelectrodes interact with the elements to transduce between acoustic andelectrical energy. The variation of potential or distance betweenelectrodes across an element causes electrical signal generation oracoustic energy, respectively.

In one embodiment, flex circuit resides between the backing block andthe PZT. The flex circuit bends around the side of the backing block andis folded (in an accordion fashion) behind the backing block. Within theflex connection bundle (accordion), the flex circuit is connected to abundle of conductors 16 that carry the signals between the beamformer 52and the array 12. In one variation, the flex connection bundle residesbetween the backing block and an insert 14 (see FIG. 6).

The elements 24 contain piezoelectric material. Solid or compositepiezoelectric materials may be used. Each element is a rectangularsolid, cube, or six sided, but other surfaces may be provided. Forexample, the emitting face 22 of one or more elements 24 is concave orconvex for elevation focusing or frequency based directivity.Alternatively, a microelectromechanical device, such as a flexiblemembrane, is used. Any now known or later developed ultrasoundtransducer may be used.

Any number of elements 24 may be provided, such as 64 elements. 128 orother number of elements 24 may allow for more or larger apertures. Theelements 24 are adjacent to each other, such as having substantiallywavelength or less spacing between the centers of adjacent elements 24.For example, the elements 24 have half wavelength spacing with kerfsacoustically separating each element 24. Sparse arrays 12 with greaterspacing between elements 24 may be used.

The elements 24 are positioned along an azimuth axis. For aone-dimensional array 12, the elements 24 are in a single row along theazimuth axis. The array 12 may be linear or curved linear. A curvedlinear array 12 has ends or a middle that extend towards or away fromthe azimuth axis, but the elements 24 are still positioned along theazimuth dimension. Due to the curve, some elements 24 of the array 12are at different depths or ranges. For use in a catheter, the azimuthaxis is generally along the longitudinal axis of the catheter 50.Generally is used as the array position within the catheter tip is theresult of rotation or translation from the axis due to tolerance ormanufacturing and/or for purposeful offset along a parallel.

Multi-dimensional arrays 12 may be used. For example, two or more rowsof elements 24 are adjacent to each other along the elevation dimension.1.25, 1.5, 1.75 or 2D arrays may be provided. The spacing betweenelements 24 along the elevation dimension is the same or different thanalong the azimuth dimension, such as a 2×64 array with half wavelengthspacing between all adjacent elements in azimuth. The elements are longin elevation, such as having a 3-20 wavelength elevation width, but maybe half wavelength or have other spacing.

The side of the elements 24 covered by the matching layer, closer to theregion to be scanned, and/or opposite the backing block is the emittingface 22. Acoustic energy is transmitted from and received at theemitting face 22 of the array 12. The angle of acoustic energy relativeto the emitting face 22 affects the sensitivity of the elements 24 tothe energy. The elements 24 are more sensitive to the energy at normalincidence to the elements 24.

Electrical conductors 16 connect the elements 24 of the array 12 to thereceive beamformer 52. The conductors 16 are cables, coaxial cables,traces, wires, flex circuits, wire jumpers, combinations thereof, orother now known or later developed conductor. One conductor 16 isprovided for each element 24. Alternatively, fewer conductors 16 thanelements 24 may be used, such as for switched apertures, partialbeamforming, or multiplexing. The conductors 16 are separatelyaddressable. Each element 24 may be selectively used for a givenaperture and associated electronic steering. Alternatively, someelements 24 are useable with only a subset of possible apertures.

The array 12 is positioned within the catheter 50. The array 12 may fitwithin a 10 French, 3.33 mm, or other diameter catheter 50. Theconductors 16 are routed through the catheter 50 to the beamformer 52.The catheter transducer is used for imaging. The images assist indiagnosis, catheter or tool guidance, and/or therapy placement.

The markers 58 in the catheter 50 are radio-opaque. Tungsten, silver,gold, stainless steel or other material may be used. The markers 58 arecylinders, but may be other shapes (e.g., spherical, conical, plate,wire, or cube). The markers 58 are any size, such as 0.5 mm diametercylinder with a 0.5 mm height.

Two markers 58 are shown in FIG. 1. In other embodiments, only one ormore than two markers 58 are used. For example, six markers 58 could beused.

The markers 58 are spaced along the catheter 50. As shown, the markers58 may be positioned adjacent to, but not behind, the array 12. Onemarker 58 is distal to the array 12, and another marker 58 is proximalto the array 12. Only proximal or only distal markers 58 are provided inother embodiments. Where more than one marker 58 is provided distal orproximal to the array 12, the markers 58 may have an even or variabledistribution, such as markers every 2-6 mm. In one embodiment, fivemarkers 58 are placed distal to the array 12 and two markers 58 areplaced proximal to the array 12. In alternative embodiments, one or moremarkers 58 are positioned under or behind the array 12. The markers 58may be beside or to the sides of the array 12 rather than or in additionto the proximal and/or distal ends.

FIGS. 2 and 3 show a system for inserting a marker 58 in a medicalultrasound imaging catheter 50. The system provides placement of themarkers 58 at desired positions during manufacture. The holes for themarkers 58 are created in the assembled catheter 50, allowing insertionof the markers 58 into the catheter 50 after formation of the catheterhousing about the array 12.

The system includes the catheter 50, a guide 60, a clamp 64, the markers58, and a measurement device. Additional, different, or fewer componentsmay be used. For example, the measurement device is not provided. Asanother example, the clamp 64 is not provided.

The guide 60 supports and/or positions the catheter 50 to guide theforming of holes for the markers 58. The guide 60 is a template thatfits over or is positionable by the catheter 50. The guide 60 is of anymaterial, such as plastic, metal, wood, or fiberglass.

In the embodiment shown in FIG. 2, the guide 60 is a sleeve. An innerbore is formed for insertion of the catheter 50. The bore iscylindrical, but may have other shapes. The outer portion of the guide60 is also cylindrical, but may have other shapes. The guide 60 maycompletely surround the catheter, allowing marker placement at anyposition. In the embodiment shown in FIG. 3, the guide 60 is a plate.

The guide 60 includes one or more holes 62. The holes 62 are spacedaround the guide 60. The holes 62 extend through at least one wall ofthe guide 60 to allow drilling access to the catheter 50. The guide 60is a drill guide or template for forming holes in the catheter 50 forthe markers 58. The guide 60 has holes 62 that guide a drill or othertool at the correct location and orientation for marker placement.

By inserting the catheter 50 into the bore, the holes 62 are alignedwith the desired locations for inserting the markers 58. A stop, such asa closed end of the guide 60, aligns the holes 62 with the catheter 50as desired. The holes 62 are positioned for forming marker holes in thecatheter 50 adjacent to the array 12, such as proximal and distal to thearray 12. The holes 62 are positioned to avoid drilling into the array12.

The array 12 is not always at the same location within the catheter 50.During construction of the catheter 50, various stresses are placed onthe array 12 relative to the housing of the catheter 50. As a result ofthese stresses, the array 12 in the catheter 50 may shift along thelongitudinal axis, rotate about the longitudinal axis, and/or rotateaway from (no longer parallel with) the longitudinal axis. As a result,the holes 62 of the guide 60 may not be positioned at consistentlocations relative to the array 12. This may be acceptable in manyembodiments.

For embodiments where a greater accuracy of position of the markers 58relative to the array 12 is desired, the guide 60 may be oversized. Forexample, the bore allows rotation about, rotation away, and/ortranslation along the longitudinal axis of the catheter 50 relative tothe guide 60. The bore is large enough to allow shifting of the catheter50 relative to the guide 60 and corresponding holes 62.

To place the array 12 at the correct position relative to the holes 62even while the array 12 is covered by the housing of the catheter 50and/or the guide 60, an acoustic target 66 is provided in the guide 60.The acoustic target 66 is a metal or other acoustically reflectivepiece. For example, the acoustic target 66 is stainless steel.Alternatively, the guide 60 is reflective and the target is moreacoustically transparent.

The acoustic target 66 is a plate or sheet of material. Other shapes maybe used, such as a wire or one or more spheres. While shown as just onepiece, multiple acoustic targets 66 may be provided. Combinations ofshapes may be used. The target 66 has any size, such as having a similararea as the array 12.

The acoustic target 66 is on a surface of the guide 60 closest to thebore or location where the catheter 50 is to be placed. Alternatively,the acoustic target 66 is embedded within the guide 60 or is on asurface spaced from the catheter 50.

The acoustic target 66 is positioned within or on the guide 60 at alocation detectable with the array 12. By acoustically measuring withthe array 12, the position of the array 12 relative to the acoustictarget 66 is determined. The array 12 may be aligned with the acoustictarget 66, aligning the array 12 relative to the holes 62.

The clamp 64 is sized and shaped to hold the catheter 50 in a positionrelative to the guide 60. The clamp 64 holds the catheter 50 with theholes 62 aligned relative to the array 12 or the catheter 50.

The clamp 64 of FIG. 2 is the bore. The bore is sized to hold thecatheter 50 in position. For example, the bore is sized to allowinsertion of the catheter 50 but establishing friction when inserting.

Other clamps 64 may be used. FIG. 3 shows another clamp 68. Two clamps68 connect with a plate 70 or other structure for supporting thecatheter 50 during forming of the marker holes. The clamps 68 hold thecatheter 50 by compression, such as using spring force, compressionfitting, being sized about a same size as the catheter 50, one or morescrews, or other clamping structure.

The clamp 68 may hold the catheter 50 relative to the guide 60. Both theguide 60 and the clamps 68 are connected with a table, ground, or otherrelatively immobile base. The same or different bases may be used. Theclamps 68 may connect through support structure with the guide 60 or maybe separately connected to the ground. The clamps 68 and/or the guide 60are moveable relative to their supporting bases.

The clamp 68 may hold the catheter 50 relative to the guide 60 invarious positions. The positions include different lateral locationsalong the longitudinal axis. A guide (e.g., tongue and groove) may beused for this translational motion. The positions include differentrotation about the longitudinal axis. The clamps 68 may be released orhave a soft enough hold that the catheter 50 may be rotated about thelongitudinal axis. The positions include different rotation from thelongitudinal axis. The clamps 68 or guide 60 may be supported by arotatable base to allow changing of the angle of the catheter 50relative to the guide 60.

The various degrees of freedom of the clamps 68 relative to the guide 60allow adjustment of the catheter 50 relative to the guide 60. Theadjustment may account for the variation in the position of the array 12within different catheters 50. Once positioned, the various moveablecomponents may be locked, such as using a brake or screw, for formingthe marker holes.

FIG. 5 shows another clamp. The clamp is a compression fitting. Forexample, the guide 60 of FIG. 2 includes threading. The threading is onan outer circumference or in the bore. A fitting with an o-ring slidesover the catheter 50 and mates with the threading. The force fromscrewing the pieces together places holding pressure on the o-ring andcatheter 50. For example, once the catheter 50 is in the desiredposition within the bore, the catheter 50 is locked into place bytightening the compression fitting. Shims, injectable foam, or otherdevices may be used to hold the catheter 50 in place during tighteningof the clamp or forming the marker apertures.

Referring again to the embodiment of FIG. 3, the catheter 50 ispositioned relative to the guide 60 and holes 62 by moving the clamp 68or clamps 68, moving the guide 60, and/or rotating the catheter 50within the clamps 68. The change in position may be determined by ameasurement device. The measurement device is configured to indicate theposition of the array 12 relative to the acoustic target 66.

In one embodiment, the measurement device is an infrared or opticalscanner. The catheter 50 is semi-transparent. Shining light through thecatheter 50 may allow a user or a system to orient the array 12. Forexample, an optical image showing the array 12 within the catheter 50 isused by a processor to identify the array 12 and control motors forpositioning the array 12 relative to the guide 60. This operation maywork without the acoustic target 66. X-rays may be used. Fluoroscopy inpatients is limited to low radiation level or short exposure times.However, more accurate X-ray imaging devices may be used in production,and such systems image the array with sufficient resolution to exactlydetermine location and orientation. While positioning the markerscorrectly is very desirable, such an imaging system may alternatively beused to determine the exact marker position relative to the array inorder to determine a correction term (e.g., deviation from desiredlocation). This information may be stored in the ultrasound system ornavigation system.

In an embodiment using the acoustic target 66, the ultrasound system isused as the measurement device. The array 12 is a sensor. The beamformer52 and image processor 54 measure the location of the acoustic target 66relative to the array 12. A coupling gel or water is placed between theoutside of the catheter 50 and the acoustic target 66. Acoustic energyis used to measure the distance and rotation of the array 12 relative tothe acoustic target 66. The rotation of the catheter 50 may be adjustedto achieve a peak or maximum signal. When the array 12 is more directlyfacing the target 66, the return signal may be greater due to theelevation focus. By alternating transmissions and reception betweendistal and proximal elements 24, the distance from the elements 24 tothe target 66 may be determined. The catheter 50 or guide 60 is rotatedto even the distances. Similarly, the end elements 24 may be used toadjust the catheter 50 by translation along the longitudinal axis. Thepeak or maximum signal indicates proper alignment.

The adjustments may be performed iteratively. A processor may controlthe adjustments or the adjustments are handled manually. The ultrasoundgenerated by the catheter 50 is used to position the acoustic array 12parallel to a planar target 66.

Once the array 12 is parallel to the target 66, the clamps 68 are lockedin position. Alternatively, a sleeve is positioned over the catheter 50and temporarily fixed into position.

With the clamps 64, 68 locked, the marker holes are formed. The guide 60guides the drill, laser, heated rod, or other device for forming themarker holes. The marker holes are formed in the housing of the catheter50 at the desired locations.

With the catheter 50 still in the guide 60 or after removing thecatheter 50 from the clamps 64, 68 and/or guide 60, the radio-opaquemarkers 58 are placed into the marker holes. The markers 58 are insertedinto the catheter 50. The marker apertures may be large enough that themarkers 58 loosely fit. Alternatively, pressure is used to insert themarkers 58 into tightly fitting marker apertures. In yet anotherembodiment, the markers 58 are heated and used to both form the markeraperture and be inserted. The markers 58 are cut from a wire ordetached.

At least some of the markers 58 are adjacent to the array 12. Themarkers 58 may contact the array, be spaced within 3 mm, or be atanother distance from the array 12.

The catheter housing is sealed over the markers 58. After sealing, thecatheter 50 may be used for imaging. Referring again to FIG. 1, thearray 12 connects to the beamformer 52 for imaging. The beamformer 52includes a plurality of channels for generating transmit waveformsand/or receiving signals. Relative delays and/or apodization focus thetransmit waveforms or received signals for forming beams. The beamformer52 connects with the conductors 16. The beamformer 52 selects anaperture including one, some, or all of the elements 24 of the array 12.Different apertures may be used at different times. The aperture isformed by using the elements 24 for transmit and/or receive operationswhile not using other elements. The beamformer 52 is operable to scanfrom a plurality of apertures formed by adjacent groups of the elements24. The apertures may walk through regular increments or skip todifferent portions of the array 12.

For scanning, the beamformer 52 electronically focuses along the azimuthdirection. A plurality of scan lines using an aperture is scanned.During receive operations, the focus may vary as a function of depth(i.e., dynamic focusing). An elevation focus is provided by a lensand/or element sensitivity, or the array 12 is not focused in elevation.In alternative embodiments, the beamformer 52 connects with elevationspaced elements for at least partial electric focusing and/or steeringin the elevation dimension.

The image processor 54 is a detector, filter, processor, applicationspecific integrated circuit, field programmable gate array, digitalsignal processor, control processor, scan converter, three-dimensionalimage processor, graphics processing unit, analog circuit, digitalcircuit, or combinations thereof. The image processor 54 receivesbeamformed data and generates images on the display 56. The images areassociated with a two-dimensional scan. Alternatively or additionally,the images are three-dimensional representations. Data representing avolume is acquired by scanning.

Using the markers 58, the array 12 may be located in other imaging. Forexample, x-rays for fluoroscopy are transmitted through the patient withthe catheter 50 in the patient. The markers 58 are radio-opaque, soappear as bright or contrast objects in the fluoroscopic image ordetected data. Since the position of the array 12 relative to themarkers 58 is known, such as based on the positioning provided by theguide 60, the location and/or orientation of the array 12 is determinedfrom the markers 58.

FIG. 4 shows a method for manufacturing a medical ultrasound imagingcatheter. The method uses the system of FIGS. 1, 2, 3, and/or 5.Additional, different, or fewer acts may be provided. For example, theclamping of act 42 is not done, but instead the catheter is held by theuser. As another example, the marker apertures are formed in act 44, butthe markers are not yet inserted in act 46 and/or the catheter sealed inact 48.

In act 40, the catheter housing is positioned relative to a template.The catheter housing covers or houses an array of ultrasound transducerelements, the associated cables, and any steering wires. Around thearray and at the tip, the catheter housing may be more rigid or thicker.

The positioning is manual or automatic. Using motors or a user, thecatheter housing is adjusted laterally and/or rotated about any numberof axes. For example, rotation about at least two axes, the longitudinalaxis and a perpendicular axis, is provided.

The positioning places apertures of the template at desired locationsrelative to the array and/or catheter housing. For example, theapertures in the template are positioned for forming holes in thehousing near to but not in the acoustic path of the array. Near may bewithin 2 mm. Other locations may be used, such as under the array orspaced from the array. Any number of apertures may be used.

In one embodiment, the catheter housing is positioned relative to thetemplate by placement in a guide. For example, a cylindrical sleeveguides the catheter housing. Stops are used to position the catheterhousing in the cylindrical housing. The catheter housing slides into theguide, such as a sleeve, until a stop prevents further sliding. Asanother example, stops are not used. Instead, the catheter housing ispositioned in one or more clamps. The clamps guide the catheter housing.

With the guide or without a guide, the array within the catheter housingis aligned relative to the template. The alignment occurs based on theguide and stops. Alternatively, the alignment is more exact, relying onthe identification of the location of the array. Using optical imaging,a sensor, or the array itself, the array is aligned with the template.For example, the signal strength, distance from a reflector, or othersignal characteristic indicates the position of the array to thetemplate or a target on the template. The information is used to alignthe array with the template.

The catheter housing, the guide, the clamps, a support base, thetemplate, and/or the holes in the template are moved for relativepositioning. The movement may be manual or by a motor or pressure (e.g.,pneumatics).

Once positioned as desired, the clamps prevent further movement. Themoveable component or components (e.g., the catheter, guide, or clamps)are locked or braked in act 42. A thumb screw may be tightened. Springactivation, bolt closing, application of pressure, or other clamping maybe used.

In one embodiment, the catheter housing is clamped. This clamping mayprevent further translation and/or rotation. A guide, the template, theclamps themselves or other component may also be locked or clamped toprevent further movement. The catheter housing is clamped in positionrelative to the template.

In another embodiment, the clamping is performed with a compressionfitting. By turning a threaded guide, closure, or other device, ano-ring may press against the catheter housing.

Once clamped, one or more marker apertures are formed in act 44. Themarker apertures are formed in the catheter housing. The apertures inthe template indicate the location and orientation of the markerapertures. Alternatively, the orientation is assumed or treated asnormal to the axis of the catheter 50. The apertures of the templateguide the formation of the marker apertures.

The marker apertures are formed by drilling, cutting, etching, melting,or other process. For example, the apertures of the template guide adrill to the catheter housing. The drill may be zeroed at any location.The position of the drill relative to the catheter housing iscalibrated. For example, the drill bit is placed in contact with thecatheter housing. Based on this location of the drill, a marker aperturemay be formed in the catheter housing or catheter to a desired depth. Adial indicator or other measurement determines the depth from the zeroedlocation. The depth may be sufficient to allow sealing of the markerwithin the catheter housing. The drill is activated to drill through thecatheter housing and into the catheter. The catheter housing may besolid other than internal components of the catheter, such as where thecatheter housing is melted or flows to fill any gaps.

In act 46, a marker is inserted within each marker aperture. The markeris inserted using a pick and place process, such as by a robot orgravity feed device. Alternatively, the markers are manually insertedinto the marker apertures.

The markers are inserted with the template in place. The markers passthrough the apertures of the template and into the marker apertures ofthe catheter housing. Alternatively, the template or guide is removed.The catheter may be unclamped and removed or may remain clamped. Themarkers are inserted into the catheter housing directly or withoutpassing through the apertures of the template.

In act 48, the catheter housing is sealed around the marker. Additionalhousing material, such as plastic (e.g., Pebax®), is added to cover themarker and hole. The material is the same or different than the materialused to form the catheter housing. Alternatively, no additional materialis added.

To seal, heat is applied. The housing material or additional material isheated to or near a melting point. The heated material flows to fillgaps and seal the hole. In alternative embodiments, a viscous material,such as ultra-violet curable silicone, is added and cured to seal. Epoxyor other sealing adhesives may be used without heating to avoid furtherchange in the array position within the catheter or further melting ofthe catheter housing.

FIG. 6 shows another embodiment of a system for manufacturing a medicalultrasound imaging catheter. The system uses an insert 14 added to thetransducer stack prior to encasing in the catheter housing 18 ratherthan markers added after encasing.

The system includes the insert 14, the array 12, cables 16, markers 58,and the catheter housing 18. Additional, different, or fewer componentsmay be provided. For example, additional markers 58 are provided.

The insert 14 is a material in addition to the transducer stack. Thetransducer stack of the array 12 includes the matching layer,electrodes, flexible circuits, and backing block. The insert 14 mayincorporate the backing block and/or signal traces for connecting theelectrodes to the cables 16 or may not. The insert extends beyond thearray, such as distally and/or proximally along the axis of the catheter50 being assembled. The insert 14 is a separate component from the array12.

The insert 14 is plastic, but other materials may be used. In oneembodiment, the insert 14 is formed from high Tg (glass transitiontemperature) plastic (e.g., PSU Tg=190 C). The melt temperature is 10degrees or more above the melt temperature of the catheter housing 18,such as being substantially higher than the melt temperature of Pebax®.The greater melt temperature may avoid compromising the marker placementduring subsequent tipping of the catheter. By having a greater melttemperature, the insert 14 does not flow or reach a melting point evenwhen the catheter 50 is heated to form the catheter housing 18. Theinsert 14 may not change shape during the plastic welding or castingused to fabricate the catheter 50.

The insert 14 includes a cavity 22. The cavity 22 is sized to form orpress fit around the array 12. Beams, walls, or other structure on atleast two sides hold the array 12 by friction, snap fit, or otherconnector. In one embodiment, the cavity 22 press fits with the array 12on four sides. The cavity 22 may instead be oversized relative to thearray 12. A connector or adhesive holds the array 12 to the insert 14,such as on a side wall or bottom surface of the cavity 22. In yet otherembodiments, the insert 14 is free of a cavity for the array 12, and thearray 12 connects to a top surface of the insert 14. The cavity 22 maybe a hole in the insert, surrounding the array 12 on only 2-4 sides.

The insert 14 is more rigid than the array 12. For example, the plasticor other material bends less in response to the same stress as the array12 along the longitudinal axis. Beams, ridges or other structure inaddition to or as an alternative to more rigid material may be used tomake the insert 14 more rigid than the array 12. By connecting theinsert 14 to the array 12, the geometry established by the insert 14 mayassist in imaging. Maintenance of the array 12 as flat, curved or someother shape within the catheter 50 may reduce imaging artifacts and/orallow sector scanning. The bow or curvature of the array 12 may beminimized by introducing the insert 14 as a reinforcing member. Theinsert 14 may reduce any curvature along the longitudinal axis of thearray or may enforce a desired curvature.

The insert 14 includes at least one, some of, or all of the markers 58for the catheter 50. The markers 58 are placed in apertures cast,drilled, or formed in the insert 14. The portion of the insert 14extending beyond the array 12 is used to support the markers. The bottomor portion under the array 12 may alternatively or additionally supportone or more markers 58. Alternatively, the markers 58 are formed in theinsert 14, such as being cast in the insert 14. In yet otherembodiments, the markers 58 are bonded to the insert 14 withoutplacement in an aperture.

None of the guides of FIG. 2, 3, or 5 would be needed where the insertincludes all of the markers. The template would not be required to placethe markers 58 already positioned within the insert 14. Additionalmarkers may be added using the template.

Since the insert is positioned and connected with the array 12, theposition of the markers 58 relative to the array is established withprecision. The insert 14 captures the array 12 during assembly of thecatheter 50, as well as to create an extended rigid body that containsthe markers 58. The markers 58 are precisely positioned prior to plasticwelding the acoustic array 12 to the catheter housing 18. Theradio-opaque markers 58 may be accurately attached to the insert 14.

The catheter housing 18 is a sleeve of plastic or other material forinsertion into a patient. For example, the catheter housing 18 is formedfrom Pebax®. Other materials may be used.

The catheter housing 18 is placed over the array 12 and insert 14, afterthe array 12 and insert 14 are connected together. The catheter housing18 slides over the array 12, insert 14, markers 58, and some of theextent of the cables 16. In one embodiment, the catheter housing 18 isplastic welded as a thermoplastic around the array 12 and insert 14.Epoxy or other bonding agent may be provided between the catheterhousing 18 and the array 12. Multiple layers of housing material may beused, such as one layer for electrical insulation and another for theouter surface of the catheter 50.

FIG. 7 is a flow chart diagram of one embodiment of a method formanufacturing a medical ultrasound imaging catheter. The method uses thesystem of FIG. 6 or other system for assembling the catheter.Additional, different, or fewer acts may be provided. For example, theacts of the method of FIG. 4 are also provided so that markers areplaced using the insert prior to forming the catheter housing and placedusing a guide after the catheter housing has been formed. As anotherexample, act 96 is not performed. Instead, the insert has more or asimilar flexibility as the array. The acts are performed in the ordershown or a different order.

In act 90, the insert is positioned adjacent to a transducer array. Forexample, the transducer array is placed or pressed into a cavity of theinsert. Fiducials, guides, rails, posts, holes, or other structures maybe provided for positioning the insert relative to the array. The insertand the array mate or slide together in one relative position.

The placement of the insert against the array positions one or moremarkers relative to the array. For example, one or more markers are inthe insert against or adjacent to the cavity. By placing the array inthe cavity, the marker is positioned adjacent to the array. The markeris adjacent to the transducer array in a distal or proximal directionrelative to the medical ultrasound imaging catheter. The marker mayinstead be beside or under the array.

In act 92, the transducer array is connected with the insert. Theconnection may be by friction, such as a press fit of the array to theinsert (e.g., cavity). Latches, snap fit, or other connectors (e.g.,screw) may be used. Alternatively or additionally, the array is bondedto the insert with adhesive. For example, the array connects to theinsert by bonding, such as with epoxy cured at room temperature orhigher temperatures (e.g., 50 degrees Celsius). After stacking theinsert with the array, the stack is pressed and cured to fix the arrayto the insert. The adhesive is applied before positioning the arrayagainst the insert. Alternatively, the adhesive is applied afterpositioning, such as for formation of the catheter housing.

The connecting fixes the transducer array to the insert. The array doesnot move relative to the insert after the fixing. The fixing occursbefore or after addition of the catheter housing. The insert connectswith the array directly or through one or more other components. Forexample, the insert is stacked with an array of matching layer,transducer material, and backing block. Conductors, such as a flexiblecircuit extend from between the transducer material and the backingblock. The bundle or accordion bundle of flexible circuit material ispositioned behind the backing block. The insert is stacked directlyagainst the backing block or the bundle or accordion of flexible circuitmaterial is between the insert and the array.

In act 94, the catheter housing is formed. The housing is formed overthe transducer array, insert, and any markers in the insert. Thetransducer array and insert are placed into the housing, such as slidinga sleeve of housing material over the array. By heating the housingsubstantially to a melting point of the housing, the catheter housingflows into gaps and over the components of the catheter. Since theinsert has a higher melting point than the Tg of the housing, the insertmaintains position relative to the array. The insert and array remainflat despite the heating of the catheter housing.

Some portions of the catheter housing 18 before assembly and/or afterassembly may be thicker. Thicker material may be used to provide morerigidity. In extruding the catheter housing, forming thicker regions maybe difficult. Thin wall sections are desired around the sides of thearray. It is difficult to move plastic via injection molding to formthick wall sections beyond the thin wall sections. The insert does notrequire thick wall sections, so the tip or housing may be easier tomanufacture. Using the insert for rigidity may avoid providing a thickerhousing for a large region that may otherwise use a thicker housing.Alternatively, thicker housing material is provided for around theinsert.

In act 96, the transducer array is maintained substantially flat. Whilethe insert and connected array may bow or bend under some stressesduring use, the array bends less or requires greater force to bend dueto the connected insert. Since the insert is more rigid than thetransducer array, the array may be held in a more consistentconfiguration (e.g., flat) during use to scan from within the patient.This added rigidity may also apply during the tipping process where highhydrostatic pressures and sometime off-axis compressive forces bend,bow, or otherwise distort the array. Fewer image artifacts may result.

While the invention has been described above by reference to variousembodiments, it should be understood that many changes and modificationscan be made without departing from the scope of the invention. It istherefore intended that the foregoing detailed description be regardedas illustrative rather than limiting, and that it be understood that itis the following claims, including all equivalents, that are intended todefine the spirit and scope of this invention.

We claim:
 1. A method for manufacturing a medical ultrasound imagingcatheter, the method comprising: positioning a formed catheter housingrelative to a template, the catheter housing housing an array ofultrasound elements, and the template including at least one firstaperture, the positioning being of the first aperture to be near but noton the array; forming a marker aperture in the catheter housing usingthe first aperture of the template; inserting a marker in the markeraperture of the formed catheter housing; and sealing the marker apertureof the catheter housing around the marker with additional material ormaterial from the formed catheter housing existing prior to theinserting, wherein the sealing is performed after the inserting into theformed catheter housing; wherein positioning comprises aligning thearray relative to the template, and wherein aligning comprises sensingwith the array a position of the array relative to the template.
 2. Themethod of claim 1 wherein the template comprises a cylindrical sleeve,and wherein positioning comprises placing the catheter housing in thecylindrical sleeve.
 3. The method of claim 2 wherein placing comprisessliding the catheter housing into the cylindrical housing until a stopin the cylindrical sleeve prevents further sliding.
 4. The method ofclaim 1 wherein forming comprises guiding a drill with the firstaperture and drilling through the catheter housing.
 5. The method ofclaim 4 wherein forming comprises zeroing the drill relative to thecatheter housing, and wherein drilling comprises drilling to apredetermined depth.
 6. The method of claim 1 wherein insertingcomprises removing the template and placing the marker into the markeraperture.
 7. The method of claim 1 wherein sealing comprises heating thecatheter housing.
 8. The method of claim 1 wherein the marker comprisesa material opaque to x-rays and wherein inserting comprises insertingthe material.
 9. The method of claim 1 further comprising: clamping thecatheter housing relative to the template with a compression fitting.10. A method for manufacturing a medical ultrasound imaging catheter,the method comprising: positioning a catheter housing relative to atemplate, the catheter housing housing an array of ultrasound elements,and the template including at least one first aperture, the positioningbeing of the first aperture to be near but not on the array; forming amarker aperture in the catheter housing using the first aperture of thetemplate; inserting a marker in the marker aperture; and sealing thecatheter housing around the marker; wherein positioning comprises:sensing, by a beamformer and image processor connected with the array,an acoustic target having a different acoustic reflectivity thanmaterial of the template supporting the acoustic target, the sensingbeing of a position of the array relative to the template, the positionindicating a first alignment of the array based on a peak in acousticresponse received by the beamformer from the array; and aligning thearray relative to the template based on the sensing.
 11. The method ofclaim 10 wherein the template comprises a cylindrical sleeve, andwherein positioning comprises placing the catheter housing in thecylindrical sleeve.
 12. The method of claim 10 wherein forming comprisesguiding a drill with the first aperture, zeroing the drill relative tothe catheter housing, and drilling through the catheter housing to apredetermined depth.
 13. The method of claim 10 wherein the markercomprises a material opaque to x-rays, and wherein inserting comprisesremoving the template and placing the marker into the marker aperture.14. The method of claim 10 wherein sealing comprises heating thecatheter housing.
 15. The method of claim 10 further comprising:clamping the catheter housing relative to the template with acompression fitting.
 16. A method for manufacturing a medical ultrasoundimaging catheter, the method comprising: positioning a catheter housingrelative to a template, the catheter housing housing an array ofultrasound elements, and the template including a plurality of guideapertures, the positioning being of the guide apertures to be near butnot on the array; forming marker apertures in the catheter housing usingthe plurality of guide apertures of the template; inserting markers inthe marker apertures; and sealing the catheter housing around themarkers; wherein positioning comprises positioning based on measurementby the array of an acoustic response of an acoustic target of thetemplate.
 17. The method of claim 16 wherein forming comprises guiding adrill with one of the plurality of guide apertures, zeroing the drillrelative to the catheter housing, and drilling through the catheterhousing to a predetermined depth.